PhD defence about the role of jellyfish in marine ecosystems

Time & Place

TimeFriday 27 October 2017, 1:00 p.m.

PlaceDTUBuilding 303A, Auditorium 45
2800 Kgs. Lyngby

The thesis

A copy of the thesis "The lives and times of jellyfish: Modelling the population dynamics and ecological role of jellyfish in marine pelagic ecosystems" is available for reading at the Institute. Please, contact PhD School Secretary Rikke Hansen, rikh@aqua.dtu.dk.

PhD Student Nicolas Azaña Schnedler-Meyer, DTU Aqua uses theoretical models to investigate jellyfish population dynamics and to develop our understanding of how jellyfish fit into marine ecosystems. On 27 October 2017 he will defend his thesis.

Jellyfish are found nearly everywhere in marine environments, and they are often considered marine ‘pests’, as they form large, unpredictable blooms that can damage fisheries, tourism and marine infrastructure.

Despite this, jellyfish have historically been largely ignored in marine science. However, interest has recently picked up due to the widespread and increasing human impact on the marine environment that have in many cases benefited jellyfish.

The study of the interactions between jellyfish and their environments is hampered by a lack of data. In his thesis, Nicolas Azaña Schnedler-Meyer investigates the use of theoretical models as a tool for creating more knowledge about the effect of characteristic traits of jellyfish, and how they can contribute to the patterns of jellyfish occurrence in the world’s oceans and the ability to form blooms.

The thesis is based on three model studies investigating the competition between fish and jellyfish, the interactions between environmental variation and jellyfish life cycles, and the evolution of three basic modes of reproduction in jellyfish polyps.

About the defence

On Friday 27 October 2017, Nicolas Azaña Schnedler-Meyer will defend his PhD thesis "The lives and times of jellyfish: Modelling the population dynamics and ecological role of jellyfish in marine pelagic ecosystems" at DTU.

The defense will take place at 1 p.m. on DTU's Lyngby Campus in building 303A, auditorium 45.

Supervisors

Principal Supervisor: Senior Researcher Patrizio Mariani, DTU Aqua

Co-supervisor: Professor Thomas Kiørboe, DTU Aqua

Examiners

Senior Researcher Asbjørn Christensen, DTU Aqua

Research Director Geir Huse, Institute of Marine Research, Norway

Professor Peter Tiselius, University of Gothenburg, Sweden

Abstract

Jellyfish are found nearly everywhere in marine environments, and have existed virtually unchanged for more than 500 million years. Despite this, they have historically been largely ignored in marine science, however, interest has recently picked up due to the widespread and increasing human impact on the marine environment that have in many cases benefited jellyfish.

Jellyfish are often considered marine ‘pests’, as they form large, unpredictable blooms that cause inconvenience or damage fisheries, tourism and marine infrastructure. The study of the interactions between jellyfish and their environments is hampered by a lack of data, however, and the use of theoretical models to investigate jellyfish population dynamics is a promising tool for increasing our knowledge of these fascinating animals.

In this thesis, we theoretically investigated the effect of characteristic traits of jellyfish, and how they can contribute to the patterns of jellyfish occurrence in the world’s oceans and the ability to form blooms.

In the first of three model studies, we investigated how a fundamental difference in the way fish and jellyfish feed affects their competition. Jellyfish have an advantage over fish in unclear water, because they are not dependent on sight to catch their prey, and we showed that this difference may explain much of the global patterns of jellyfish occurrences.

In the second study, we investigated the interactions between environmental variation and jellyfish life cycles. We found that observed patterns of jellyfish blooms can indeed be explained by different types of variation, and predicted different responses of the two main jellyfish life cycles to seasonality and other key environmental factors.

In the last study, we investigated the evolution of three basic modes of reproduction in jellyfish polyps; a small bottom-dwelling life stage of most jellyfish that is important for their ability to bloom. Consistent with observations, our evolutionary model predicted the evolution of more than one strategy in most cases, and we predicted how each strategy should be favored by different environmental effects.

Developing our understanding of how understudied, but important, groups like jellyfish fit into marine ecosystems, and how they depend on environmental conditions, is a pressing task, as human pressures on the marine environment are only expected to increase in the future.

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